1. Field of the Invention
The present invention relates to a feeder for feeding a recording medium in an image forming apparatus such as a copying machine, a laser printer, a facsimile, etc.
2. Description of the Related Art
In a known image forming apparatus such as a copying machine, a sheetlike recording medium such as a sheet of transfer paper is fed by the friction of a roller made of rubber and is conveyed by a pair of rubber rollers, a belt, etc. to an image forming position such as a transfer position with respect to a photosensitive body.
In such a general feeder for feeding and conveying the recording medium, a frictional pad is combined with the feed roller made of rubber to prevent a plurality of recording media from being fed in an overlapping state. A reversing roller made of rubber may be combined with the feed roller to turn the recording media upside down. Further, a corner claw may be disposed in a cassette for storing the recording media. However, in a general recording system, a recording medium is jammed and slantingly fed in a feeding operation thereof. Accordingly, the general feeder has problems about reliability of the feeding and conveying operations of the recording medium in addition to the overlap-feeding operation of the recording media.
Further, the general feeder has a complicated structure and a control operation of the general feeder is complicated so that cost of the feeder is increased. Accordingly, no problems about the simplified structure and the reduction in cost are solved in the general feeder.
To solve these problems about the general feeder, an insulating endless belt is approximately wound around an entire conveying system disposed within the copying machine and is charged by a charging means. A sheet of paper stored in a paper feeding tray is fed by a paper feed roller coaxially disposed with a belt support roller. Thereafter, the sheet of paper is electrostatically adsorbed to the belt. Otherwise, the belt directly comes in contact with the sheet of paper. Thus, the sheet of paper is fed by the belt in a state in which the sheet of paper is electrostatically adsorbed to the belt. Simultaneously, the sheet of paper comes in contact with the photosensitive body and is conveyed by the belt to a transfer region for performing a transfer operation. For example, such a structure is proposed and shown in Japanese Patent Application Laying Open (KOKAI) Nos. 59-212856, 59-224858 and 59-229585, etc.
However, in such a general structure, the sheet of paper is fed by a frictional contact between the paper feed roller and the sheet of paper when the sheet of paper stored in the paper feeding tray is fed out of this tray by the paper feed roller coaxially disposed with a drive shaft of the insulating endless belt. Accordingly, the sheet of paper is slantingly fed in a certain case. When some sheets of paper are simultaneously fed in an overlapping state, a first or upper sheet of paper is conveyed in a state in which the first sheet of paper is electrostatically adsorbed to the belt. In contrast to this, lower second and subsequent sheets of paper fed together with the first sheet of paper are projected from a front end of the paper feeding tray. Therefore, a paper jam is caused when the next paper feeding operation is performed.
Further, paper powder is generated by the above frictional contact so that an error in the paper feeding operation is caused and a reduction in image quality is caused when an image is formed.
When the sheet of paper stored in the paper feeding tray is directly fed by the charged insulating endless belt, the belt comes in contact with the sheet of paper in a state in which the belt is moved and turned in the normal image formation. Accordingly, a contact state between the belt and the sheet of paper becomes unstable unless tension of the belt, a lowering state of the belt, and loading and arranging states of the sheet of paper are uniformed with considerable accuracy. In such a case, the sheet of paper tends to be slantingly fed.
It is necessary to arrange the belt and the sheet of paper within the feeder with high accuracy so as to stabilize the contact state between the belt and the sheet of paper.
The belt and the paper feed roller come in contact with the first sheet of paper in a turning state between the first and second sheets of paper (i.e., the upper and lower sheets of paper). Therefore, frictional force having a certain strength is caused so that there is a fear of generation of the overlap-feeding operation of sheets of paper.
Further, the belt in the turning state comes in contact with the sheet of paper although no sheet of paper is separated and discharged by friction. Accordingly, frictional force is caused in a discharging portion of the sheet of paper, thereby generating a certain amount of paper powder.
As mentioned above, a conveying state of the sheet of paper from the paper feeding tray is not constant and reliable at any time although the paper feed roller or the belt is used as a paper feeding means. Accordingly, it is necessary to dispose a resisting means for adjusting positions of a front end of the paper sheet and a front end of an image copied on the paper sheet and correcting an inclination of the paper sheet. Therefore, the general feeder has a complicated structure and a control operation of the general feeder is complicated.
A paper feeding section of the copying machine, a resisting section, a transfer section, a fixing section and a paper discharging section are sequentially connected to each other through a single endless belt. First, the endless belt comes in press contact with a sheet of copying paper held by the copying paper feeding section. The sheet of copying paper is then discharged by frictional force from the copying paper feeding section. After a resisting operation of the sheet of paper, the sheet of paper is conveyed to an image forming region. For example, such a structure is proposed and shown in Japanese Patent Application Laying Open (KOKAI) No. 63-139846. In this paper feeder, when a sheet of paper stored in the copying paper feeding section such as a paper feeding tray is fed by the belt, the paper feed roller separates the sheet of paper therefrom by a frictional contact and feeds this sheet of paper. Accordingly, the PG,8 sheet of paper is slantingly fed and some sheets of paper are fed together in an overlapping state in a certain case. Further, paper powder is caused by the frictional contact. Therefore, an error in the paper feeding operation is caused and a reduction in image quality is caused when an image is formed. A feeding state of the sheet of paper from the paper feeding tray is not constant and reliable at any time. Accordingly, it is necessary to dispose a resisting means for adjusting positions of a front end of the paper sheet and a front end of the image copied on the paper sheet and correcting an inclination of the paper sheet. Therefore, this general feeder has a complicated structure and a control operation of this feeder is complicated.